A good example of Osborn's difficult-to-understand conception of evolution can be seen in his "The Ancestral Tree of the Proboscidea: Discovery, Evolution, Migration, and Extinction Over a 50,000,000 Year Period" read before the National Academy of Sciences in 1935. In this paper Osborn attempted to summarize his research on trends in the evolution of extinct brontotheres and proboscideans (i.e. elephants and their closest extinct relatives), which he believed exemplified two great evolutionary principles;
1. The older modes known to naturalists from the time of Aristotle to that of Darwin, namely, changes of proportion or of degree which we term ALLOIOMETRONS; alloiometrons are governed by the action of the four well-known energetic factors, subject to Natural Selection.
2. Creative changes of kind, the origin of absolutely new characters, which we term ARISTOGENES, new adaptations arising directly from the geneplasm, e.g., the horns of Titanotheres and the innumerable new cones, crests and other elements in the teeth of Proboscideans.
For Osborn natural selection was weak. It could act upon variations but it was not a creative evolutionary force. Instead Osborn thought that new traits, or what he called "aristogenes" were carried along, ready for expression, in the genetic material of the animal and popped up suddenly. In this way there was a sort of
evolutionary inertia where, eventually, a particular form was almost inevitable as the parts necessary to form it were inherent in the genes of the organism all along.
Osborn was not suggesting that his "aristogenes" were macromutations that were then acted upon by natural selection. The new traits were already fine-tuned to what the creature needed to survive. Thus, for Osborn, "artistogenes" were by definition adaptive. Later in the same paper he wrote;
A new aristogene is readily distinguished from a new D. mutation [i.e. a sudden, large-scale mutation that gives rise to a new trait] by invariably obeying the eighteen principles of biomechanical adaptation; D. mutations on the contrary may or may not be adaptive.
This may seem straightforward now, but let me assure you it took a lot of careful reading to tease this much out. While Osborn did make many important contributions to paleontology his ideas about evolution, especially in his later years, were often presented in a tangle of new terms and references to certain laws or principles. It seemed like he was trying to make his hypotheses more law-like by forming new terms and trying to boil them down to the workings of chemistry and physics, but it seems to me that this approach backfired.
This blog was reposted with permission from Laelaps
, a blog created by Rutgers University student Brian Switek, who writes about paleontology, evolution, and the history of science.
Image Caption: Osborn's view of the progressive evolution of the brontotheres. Notice the references to the "geneplasm" at left, which Osborn interpreted as spontaneously giving rise to new adaptations. From Osborn (1935).